From ed9571f0cf1fe09d3506302610f3ccdfa1d22c4a Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Fri, 13 Dec 2013 14:55:55 +0000 Subject: [PATCH] dm array: fix a reference counting bug in shadow_ablock An old array block could have its reference count decremented below zero when it is being replaced in the btree by a new array block. The fix is to increment the old ablock's reference count just before inserting a new ablock into the btree. Signed-off-by: Joe Thornber Signed-off-by: Mike Snitzer Cc: stable@vger.kernel.org # 3.9+ --- drivers/md/persistent-data/dm-array.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/drivers/md/persistent-data/dm-array.c b/drivers/md/persistent-data/dm-array.c index af96e24ec328..1d75b1dc1e2e 100644 --- a/drivers/md/persistent-data/dm-array.c +++ b/drivers/md/persistent-data/dm-array.c @@ -317,8 +317,16 @@ static int shadow_ablock(struct dm_array_info *info, dm_block_t *root, * The shadow op will often be a noop. Only insert if it really * copied data. */ - if (dm_block_location(*block) != b) + if (dm_block_location(*block) != b) { + /* + * dm_tm_shadow_block will have already decremented the old + * block, but it is still referenced by the btree. We + * increment to stop the insert decrementing it below zero + * when overwriting the old value. + */ + dm_tm_inc(info->btree_info.tm, b); r = insert_ablock(info, index, *block, root); + } return r; } -- 2.34.1